A reader commented about my add-ons screenshot, that I was running OpenDownload 1.0.0 which has not been updates since January 2007 (Firefox 2.0.0.1 was the newest release back then). I’ve been forcing the extension to work either via Nightly Tester Tools or Add-on Compatibility Reporter. Oddly enough, this has worked fine over the last nearly 5-years, especially when so many old extensions broke when Firefox 4 was released this past March. They did point me in the direction of OpenDownload², which is an experimental add-on to replace the original OpenDownload from 2007.
OpenDownload² was last updated in April 2011 and works with Firefox 3.6 through Firefox 8.0. However, it can be forced to work with Firefox 9 and higher using the Add-on Compatibility Reporter.
I’ve been using Open In Browser for this for some time:
http://spasche.net/openinbrowser/